Range-Angle Estimation Using FDA-MIMO Radar With Inter-Pulse Coding Modulation

Frequency diverse array (FDA)-multiple-input and multiple-output (MIMO) radar can form angle-distance 2D beam pattern, which has good anti-jamming ability. This paper proposes a towed jamming suppression method based on FDA-MIMO radar. The minimum variance spectral estimation (MVSE) algorithm is used to accurately locate the target and the jamming location, and then the target and the jamming are identified based on the difference in Doppler frequency. Finally, the minimum variance distortionless response (MVDR) adaptive beamforming algorithm suppresses jamming. In addition, this paper selects the square frequency increment instead of the commonly used linear frequency increment, so that the beam has a better range resolution to obtain a better anti-jamming effect. The simulation results prove the effectiveness of the method proposed in this paper.

This paper proposes a method to enhance direction of arrival (DoA) estimation accuracy and resolve range ambiguity in interleaved subcarrier-based multiple-input multiple-output (MIMO) single carrier-frequency division multiple access (SC-FDMA) systems for radar applications. Using the virtual array in the MIMO configuration, a large effective aperture can be synthesized using a relatively small number of transmitting and receiving antenna elements, enabling high angular resolution. To realize this virtual array, orthogonality among multiple transmitters must be ensured. For instance, the interleaved subcarrier allocation scheme enables signals from multiple transmitting antenna elements to be orthogonal. However, this allocation introduces range-dependent phase shifts between transmitting antenna elements, which degrade DoA estimation accuracy, and reduces the maximum unambiguous detection range. To mitigate these problems, we propose a method to compensate for the phase shift in each virtual array, along with a range ambiguity resolution method based on phase linearity analysis. The proposed methods are validated through simulations. With the proposed method, the average DoA estimation error is reduced from 5.63° to 0.2°. Furthermore, the proposed method successfully resolves range ambiguity, reducing the estimation error to 0 m for a target at 1500 m, which lies beyond the system’s maximum unambiguous range of 384 m. The results confirm that the proposed approach improves DoA estimation accuracy and resolves range ambiguity in interleaved MIMO SC-FDMA systems.

Multiple-input multiple-output (MIMO) radar enjoys the advantage of increased degrees-of-freedom and spatial diversity gain, but it cannot effectively resolves the targets closely spaced in the same angle cell (but different range cells). Frequency diverse array (FDA)-MIMO radar can handle this problem by exploiting its range-dependent beampattern. FDA-MIMO radar was, thus, suggested for range–angle estimation of targets. Nevertheless, it is necessary to provide theoretical performance analysis for such a relatively new radar technique. Since multiple signal classification (MUSIC) algorithm is widely adopted in most of the FDA-MIMO literature, this paper derives the Cramer–Rao lower bound and mean square error expressions in MUSIC-based range–angle estimation algorithms for a general FDA-MIMO radar. Furthermore, the corresponding range and angle resolution thresholds in target detection and localization are also derived. Numerical results verify that the FDA-MIMO indeed outperforms conventional MIMO radar in both range–angle estimation and resolution threshold performance.

In recent years, the frequency diverse array (FDA) radar has attracted much attention due to its range-angle dependent beam-pattern. And multiple input multiple output (MIMO) radar has been widely investigated with the advantage of transmit waveform diversity. In this paper, a FDA-MIMO Inverse Synthetic Aperture Radar (ISAR) is proposed to achieve anti-jamming of ISAR imaging. LFM (Linear Frequency Modulated) and SFCS (Stepped-Frequency Chirp Signal) signals are transmitted to jammer and targets respectively, and the received signals are matched filtering by the signal transmitted to the targets. So the jamming signal can't matched with the reference signal, the well anti-jamming effect can be obtained. The performance of the proposed method is evaluated by the simulation results.

To avoid the disadvantages of the active radar which utilizes its own transmitter to emit electromagnetic radiations, passive radars use the signals readily available in the environment and can provide superior capabilities of stealth target detection, low probability of intercept, low cost, and robustness. This paper investigates the joint target parameter (delay and Doppler) estimation performance for a frequency modulation (FM)‐based distributed passive radar network (DPRN) system with antenna arrays. The DPRN system consists of multiple FM‐based illuminators of opportunity and multiple radar receivers, which are placed on moving platforms. First, we consider the scenario where the target state parameters are unknown, the maximum likelihood estimator is developed, and the log‐likelihood ratio of the received signal for a complex Gaussian extended target is derived. Then, the Cramér‐Rao lower bounds (CRLBs) on the Cartesian coordinates of target position and velocity are computed for a DPRN system with MT FM‐based transmitters of Q antenna elements and MR multichannel receivers of P antenna elements. Finally, numerical examples demonstrate that grouping the receiving antenna elements into properly sized arrays can reduce estimation errors. It is also shown that the joint CRLB is a function of signal‐to‐noise ratio, the number of receiving antenna elements, the properties of the transmitted FM waveform, and the relative geometry between the target and the DPRN architecture. The analytically closed‐form expressions for CRLB are an important performance metric in that they enable the optimal placement of radar receivers to improve the target parameter estimation performance.

Radar parameter estimation in terms of its range, angle and velocity plays a crucial role in many applications. Multiple-input multiple-output (MIMO) radar with frequency diverse array (FDA) is capable of resolving targets in one directional beam with different ranges and velocities (Doppler shifts). Prevalent methods obtain target parameters in a sequential manner to get rid of exhausted multi-dimensional search, but they suffer from accumulated estimation errors. To tackle this issue, a tensor generalized weighted linear predictor (TGWLP) is devised for FDA-MIMO radar parameter estimation, where the parameters are estimated in a parallel manner. Tensor modeling of multidimensional FDA-MIMO radar signal is developed, so that the joint parameter estimation is casted into multiple-pulse-group version of three-dimensional (3D) HR problem associated to the mixed Swerling model. Pulse-group diversity is exploited to obtain precise velocity estimation. In the presence of targets with some identical parameters, the final estimations of unambiguous slant range, conic angle, and radial velocity of a moving target can be easily obtained after the parallel frequency estimations. Besides, all the parameter pairing is automatically achieved, which is free of the extra burden from pairing process. Furthermore, the identifiability of the proposed joint estimator is analyzed. Finally, theoretical analysis and simulations are included to demonstrate that the proposed approach can achieve improved performance compared to the existing methods.

Range ambiguity has always been an inherent problem in pulse instrumentation radar system. At present, the traditional resolving range ambiguity algorithm is generally based on the Remainder Theorem. However, when radar detects medium or high orbit space target, the signal-to-noise ratio of the radar echo is low because the space target is far away and its radar cross section is small. In this case, the efficiency of the traditional resolving range ambiguity algorithm is reduced and even the algorithm cannot be applied. Therefore, in order to solve the problem of range ambiguity in the condition of low SNR radar echo, a coherent accumulation resolving range ambiguity algorithm based on chirp rate polarity modulation with M-sequence is proposed. In this algorithm, the M-sequence is used to modulate the chirp rate polarity of radar transmitting signal (chirp signal). Then the radar echo signal is compressed by reference matching filtering. Finally, the sliding window coherent accumulation process is applied to resolving the radial range ambiguity of space target. The simulation experiment shows that the proposed algorithm can improve the resolving range ambiguity efficiently, which is especially suit for engineering application.

A clustering algorithm is compared to and found superior to the Chinese remainder theorem for resolving range ambiguities. The clustering algorithm provides a significant improvement in performance. It is demonstrated that it is easier for medium pulse repetition frequency (PRF) than for high-PRF waveforms to resolve all the range-Doppler ambiguities. >

Different from traditional multiple-input and multiple-output (MIMO) radar, the frequency diverse array MIMO (FDA-MIMO) radar generates beampattern that is dependent on both range and angle, making it applicable for joint range–angle estimation of targets. In this paper, we propose a novel time reversal based FDA-MIMO (TR-FDA-MIMO) approach for target detection. Based on the time reversal theory, the TR-FDA-MIMO signal model is established, the TR transmitting–receiving and signal processing procedure are analyzed, and the resulting range–angle spectra for targets imaging are acquired by utilizing the multiple signal classification algorithm. Numerical simulations are carried out for both single and multiple targets cases. The imaging resolution and robustness to the noise of the proposed approach are investigated and results are compared with conventional FDA-MIMO radar. It turned out that by cooperating with TR, the performance of FDA-MIMO radar for target range–angle estimation is effectively enhanced, consequently improving its applicability in practical target-detecting cases.

Range ambiguity is a serious problem existing in the wide swath SAR imaging due to the impact of high pulse repetition frequency. To address this problem, this paper proposes a new imaging configuration via using the frequency diverse array (FDA) antenna. By designing the frequency increment along array elements and adopting the sub-array technique, FDA can easily allocate its beam to the corresponding unambiguous block, which outperforms the conventional methods. The FDA generated range-dependent phase shift can be used to extract the signal from different range block, accomplishing range unambiguous focusing. Simulation results are provided to demonstrate the effectiveness of the proposed approach.

In medium pulse repetition frequency (MPRF) radars, ambiguities exist both in range and Doppler measurements. Some efficient techniques have been established to resolve the range and velocity ambiguity of the target using multiple PRF. In this paper, a simple algorithm is proposed to resolve both range and velocity ambiguity based on residue arithmetic. This algorithm makes out the unambiguous result by using a residue look-up table. The particular problem of filter bandwidth unitary frequency is settled and assessed with another algorithm. An example for the generation of the residue took-up table is presented to resolve range ambiguity.

Low observable moving target-detection technology under clutter background is the key factor affecting the radar performance. Here, frequency diverse array (FDA) MIMO radar is investigated for low-observable moving target detection. FDA-MIMO radar not only has all the advantages of phased array and MIMO radar, but also can make a two-dimensional joint estimation of the target distance and azimuth. In order to achieve coherent integration for Doppler processing, a novel three-dimensional processing method is proposed, i.e. space-range-Doppler focus (SRDF) processing. It utilises the property of FDA and high-resolution Doppler processing of MIMO. After discussing signal model of FDA-MIMO radar, the flowchart of SRDF-based low-observable moving target detection and estimation is provided. Finally, simulation of moving target detection in clutter background verifies that proposed method has better ability for joint angle-range-Doppler processing with higher resolutions.

Frequency diverse array (FDA) has its unique advantage in realizing low probability of intercept (LPI) technology for its dependent beam pattern. In this paper, we proposed a cognitive radar based on the frequency diverse array multiple-input multiple-output (MIMO). To implement LPI of FDA MIMO transmit signals, a scheme for array weighting design is proposed, which is to minimize the energy of the target location and maximize the energy of the receiver. This is based on the range dependent characteristics of the frequency diverse array transmit beam pattern. To realize the objective problem, the algorithm is proposed as follows: the second-order nonconvex optimization problem is converted into a convex problem and solved by the bisection method and convex optimization. To get the information of target, the FDA MIMO radar is proposed to estimate the target parameters. Simulation results show that the proposed approach is effective in decreasing the detection probability of radar with lossless detection performance of the receive signal.

Different from phased array providing only angle‐dependent transmit beampattern, frequency diverse array (FDA) employs a small frequency increment across its array elements to provide range–angle‐dependent transmit beampattern. This enables the array beam to scan without the need of phase shifters or mechanical steering. Since FDA has received much attention in antenna and radar signal processing societies, it is necessary to make an overview on this interesting topic. This study introduces what FDA is and why it could be exploited for radar and navigation applications from a top‐level system description and appeal to the radar signal processing and system engineering communities for more investigations on this promising array technique. The status of FDA studies is overviewed and the most recent advances of FDA radar are discussed. The basic FDA system architectures are introduced, along with performance compared to a conventional phased‐array. Next, guidelines for choosing good system parameters and typical implementation schemes are provided. Finally, potential applications in range and angle estimation of targets, cognitive FDA radar and low probability of identification FDA radar are discussed, along with several technical challenges.

To meet the urgent demand of low-observable moving target detection in complex environments, a novel method of Frequency Diverse Array (FDA) radar signal processing method based on Space-Rang-Doppler Focusing (SRDF) is proposed in this paper. The current development status of the FDA radar, the design of the array structure, beamforming, and joint estimation of distance and angle are systematically reviewed. The extra degrees of freedom provided by FDA radar are fully utilizsed, which include the Degrees Of Freedom (DOFs) of the transmitted waveform, the location of array elements, correlation of beam azimuth and distance, and the long dwell time, which are also the DOFs in joint spatial (angle), distance, and frequency (Doppler) dimensions. Simulation results show that the proposed method has the potential of improving target detection and parameter estimation for weak moving targets in complex environments and has broad application prospects in clutter and interference suppression, moving target refinement, etc..